1. Field of the Invention
This invention relates to an image forming apparatus for forming an electrostatic latent image in an image bearing body and developing the electrostatic latent image with developer stored in a developing apparatus, and more particularly to an image forming apparatus having a remaining developer amount detecting device provided with remaining developer amount detecting means capable of serially detecting the remaining amount of developer stored in a developer container as well as a cartridge that can be inserted in the image forming apparatus main body, that is, a process cartridge, a developing apparatus constituted as a cartridge.
Here, for example, an image forming apparatus using electrophotography technology includes an electrophotographic copying machine, an electrophotographic printer, such as an LED printer, a laser beam printer and the like, an electrophotographic facsimile apparatus and so on.
In addition, a process cartridge refers to a cartridge integrally constituted by at least one of charging means, developing means and cleaning means, and an electrophotosensitive body, which is made detachably attachable to an electrophotographic image forming apparatus main body, or a cartridge integrally constituted by at least developing means and an electrophotosensitive body, which is made detachably attachable to an electrophotographic image forming apparatus main body.
2. Related Background Art
In a conventional image forming apparatus using, for example, an electrophotographic image forming process, a process-cartridge method is adopted in which the cartridge is integrally constituted by an electrophotographic sensitive body and process means affecting the electronic electrophotosensitive body and is made to be detachably attachable to an electrophotographic image forming apparatus main body. In accordance with the process-cartridge method, since the maintenance of the apparatus can be conducted by a user in person and not by a serviceman, the operability is considerably improved. Hence, the process-cartridge method is widely used in electrophotographic image forming apparatuses.
In an electrophotographic image forming apparatus using a process-cartridge method, although an image can be formed again by replacing a cartridge when developer is exhausted, the replacement of a cartridge should be performed by a user in person and, therefore, means for warning a user when developer is exhausted, i.e., a remaining developer amount detecting device, is required.
A remaining developer amount detecting device has remaining developer amount detecting means that can detect a remaining-developer-amount level in a cartridge or an image forming apparatus main body in order to make it possible to find at any time how much developer is left to serve to form images in the cartridge.
There is the flat antenna method as one method of this remaining developer amount detecting means. A flat antenna, as shown in FIG. 3, has a pair of conductor patterns 22, 23 having a predetermined interval therebetween and formed on a substrate 21, which are disposed in a position contacting developer on an inner side of a developer container and, as the amount of developer in the developer container decreases, the contacting area of the developer and the flat antenna 20 also decreases.
The electrostatic capacity varies as the contacting area of the conductor pattern surface and the developer changes due to the consumption of the developer, and this makes it possible to represent the relationship between the remaining developer amount in the container and the electrostatic capacity of the flat antenna, and the remaining developer amount in the container can be found at any time by measuring the electrostatic capacity of the flat antenna.
The electrostatic capacity of the flat antenna 20 is obtained by applying a constant alternate current bias on one of the pair of conductor portions 22, 23 and detecting the current flowing to the other conductor part at that time.
In fact, since there is a slight remaining developer sticking to the surface of the flat antenna 20 even if the developer in the developer container decreases little by little, the surface of the flat antenna is cleaned as an agitating member rotates with an antenna cleaning member attached to the agitating member provided in the developer container.
However, the output of the flat antenna 20 changes in a cycle in accordance with the timing at which the cleaning member cleans the antenna surface, by cleaning the antenna surface in this way. Thus, the remaining developer amount level is confirmed by statistical processing, such as finding the average value or choosing the minimum value depending on the cycle.
However, even if the remaining developer amount detecting means such as the flat antenna 20 capable of detecting the remaining developer level is provided as described above, the remaining developer amount level cannot always be found. For example, immediately after the power from a power source of the image forming apparatus main body is inputted, the remaining developer amount in the cartridge is unknown. A certain length of time is required until a measurement result is obtained because it is not until the apparatus is made to operate such as to form a certain number of images that the remaining developer amount level is confirmed.
Therefore, immediately after power from the power source of the image forming apparatus main body is inputted, immediately after a cartridge is once taken out and inserted again for jam processing or in other similar cases, there is a problem that the user cannot immediately find if there is a developer amount sufficient for a number of pieces of papers to be printed in the cartridge.
In addition, there is a possibility that the remaining developer amount detecting means such as the flat antenna 20 capable of detecting the remaining developer amount level breaks down. Causes of failures might be electronic failures, such as a defective contact and a defective application bias or mechanical failures, such as damage to the flat antenna 20. In any case, the possibility that both the image forming apparatus and the cartridge are critically affected is high.
Therefore, it is desired that whether the remaining developer amount detecting means breaks down or not is made to be detectable immediately after inserting a process cartridge in the image forming apparatus, and at least before the image forming apparatus forms an image and that both the image forming apparatus and the cartridge are prevented from being affected critically.
A similar problem occurs when the remaining developer amount in a developer container provided in the image forming apparatus main body or in developer container and the like of the developing apparatus constituted as a cartridge is detected by the remaining developer amount detecting means.